Interesting discussion.

Some governments did seem able to retain control of provinces: Rome seemed to hang onto a province once conquered. , so they gradually accumulatedna empire. I think Babrabian tribes m,ight be less able to do this, and even some monarchies (eg Epirus) had trouble holding more than a handfyul of provinces together. Of course this is related to manpower, wealth but also administrative capacity. Makedonia spread and contracted several times from Phillip II to Perseus. A strong King with able FMs and generals built an empire, then huie died and itr fell apart. This doesn't happen so well in the TW engine atm.

Could the Romans (and other able administrators) be given an adapted agent (say change the princess unit) as a pacifying "governor" agent, so they can more easly control more provinces? Maybe they could also assist with cultural conversion.

I'm not saying we should deny this to the "barbarians" but they wouldn't start with it: if the Casse want an efficient provincial system they will have to build some monster administrative building/building sequence in the capital, maybe after they get certain reforms.

Romahs might strart one level into the administrative tree producing "governors", others with no levels. That way an active Casse or Arverni could be as conquiest happy as they liked 9and maybe score a bit of loot) but they'd quicklly lose the new provinces to revolts, unless they built the adminitrative expertise to hold their conquests.

I know FMs are governors in cities, but this would be a supplementary agent to represent colonial efficiency.

Just a thought.